The present invention relates to a method of manufacturing a spin valve film that is one type of a magnetoresistance effect element. The invention also relates to a method of manufacturing a magnetoresistance-effect magnetic lead that incorporates such a spin valve film as a magnetism-sensitive element for detecting magnetic signals emanating from magnetic recording media.
Magnetoresistance effect elements (hereinafter referred to as MR elements) make use of so-called xe2x80x9cmagnetoresistance effect,xe2x80x9d i.e., a change in resistance, which results from a change in the intensity and direction of an external magnetic field. For example, MR elements are used for magnetic heads as magnetism-sensitive elements for detecting a signal magnetic field from magnetic recording medium. Magnetic heads comprising an MR element are generally known as xe2x80x9cmagnetoresistance-effect magnetic headsxe2x80x9d (hereinafter referred to as MR heads).
MR elements utilizing anisotropic magnetoresistance effect have hitherto been used. They have but a small rate of change in magnetoresistance (MR ratio). It is therefore desired that MR elements having a large MR ratio be provided.
Giant MR elements (hereinafter referred to as xe2x80x9cGMR elementsxe2x80x9d), each using a spin valve film, are proposed as MR element having a large MR ratio.
A GMR element has a spin valve film that comprises a pair of magnetic layers and a nonmagnetic layer interposed between the magnetic layers. It makes use of so-called xe2x80x9cgiant magnetoresistance effect, i.e., a change in the conductance of a so-called xe2x80x9csense currentxe2x80x9d that flows in a surface of the spin valve film, which depends upon the relative angle between the axes of magnetization of the magnetic layers.
More specifically, a spin valve film comprises an anti-ferromagnetic layer, a magnetization-fixed layer, a magnetization-free layer, and a nonmagnetic layer, which are laid one upon another. The magnetization-fixed layer has been magnetized in a prescribed direction when an exchange-coupling magnetic field acting between it and the anti-ferromagnetic layer. The magnetization-free layer has its magnetization direction changed in accordance with the external magnetic field. The nonmagnetic layer magnetically isolate the magnetization-fixed layer and the magnetization-free layer from each other.
When an external magnetic field is applied to the GMR element, the magnetization direction of the magnetization-fee layer changes in accordance with the intensity and direction of the external magnetic field. When the magnetization direction of the magnetization-free layer becomes anti-parallel to the magnetization direction of the magnetization-fixed layer, the sense current flowing in the spin valve film reaches the maximal value. When the magnetization direction of the magnetization-free layer becomes parallel to the magnetization direction of the magnetization-fixed layer, the sense current flowing in the spin valve film reaches the minimal value.
When a sense current of a prescribed value is supplied to a magnetic head comprising such a GMR element (hereinafter referred to as xe2x80x9cGMR headxe2x80x9d), the sense current flowing in the GMR element changes in terms of voltage in accordance with the signal magnetic field from the magnetic recording medium. The change in the voltage of the sense current is detected, whereby a magnetic signal can be read from a magnetic recording medium.
The GMR head needs to have its MR ratio increased, in order to record data at higher densities on magnetic recording media. To this end, the Cu film that is the nonmagnetic layer of the spin valve film may be made thinner.
If the Cu film, i.e., the nonmagnetic layer, is made thinner, however, the inter-layer coupling between the magnetization-fixed layer and the magnetization-free layer will increase. This makes it difficult to set a bias point in the course before the head operates.
It is required that the Cu film be about 26 xc3x85 or more thick so that the inter-layer coupling may become, for example, 20 Oe or less. The Cu film cannot help but have high conductivity and allows the passage of a large current. This gives rise to a large split loss. Consequently, the MR ratio of the spin valve film decreases very much.
Recent studies show that, when a Cu film to be processed into a nonmagnetic layer is formed by means of sputtering at a reduced pressure in the chamber of a sputtering apparatus, the surface smoothness of the Cu film was enhanced by virtue of the pressures and compositions of the residual gas, such as oxygen, hydrogen or the like. On the other hand, the static magnetic coupling between the magnetization-fixed layer and the magnetization-free layer, which depends upon the surface roughness of the Cu film, decreases to reduce the inter-layer coupling. That is, the inter-layer coupling between the magnetization-fixed layer and the magnetization-free layer can be lowered by decreasing the degree of vacuum in the chamber, rather than by raising the degree of vacuum.
However, the method of decrease the inter-layer coupling between the magnetization-fixed layer and the magnetization-free layer by using the residual gas in the chamber can hardly be practiced because it is difficult to maintain the residual gas in the same state. The method can hardly improve the productivity.
The residual gas in the chamber may be maintained in the same state in terms of composition, back-pressure and the like. Even in this case, if the degree of vacuum is degraded, the anti-ferromagnetic layer of the spin valve film is degraded in characteristics. If the anti-ferromagnetic layer is made of PtMn, PdPtMn or the like, which is most commonly used Mn-based anti-ferromagnetic material, it can acquire good characteristics and can be thin by raising the degree of vacuum in the chamber.
Therefore, spin valve films are usually formed at a high vacuum in the chamber so that the anti-ferromagnetic film is to acquire good characteristics. It is extremely difficult, however, to make the Cu film (i.e., the nonmagnetic layer) as thin as desired, without increasing the inter-layer coupling between the magnetization-fixed layer and the magnetization-free layer.
The present invention has been made in view of the foregoing. An object of the invention is to provide a method of manufacturing a spin valve film, in which the inter-layer coupling between the magnetization-fixed layer and the magnetization-free layer can be suppressed even if the Cu film, i.e., the anti-ferromagnetic layer, is thin, and the anti-ferromagnetic layer can be formed at a higher vacuum than before. Another object of this invention is to provide a method of manufacturing a magnetoresistance magnetic head incorporating such a spin valve film as a magnetism-sensitive element for detecting magnetic signals emanating from magnetic recording media.
To achieve the first object, a method is provided, which is designed to manufacture a spin valve film comprising an anti-ferromagnetic layer, a magnetization-fixed layer magnetized in a prescribed direction by an exchange coupling magnetic field acting between it and the anti-ferromagnetic layer, a magnetization-free layer having a magnetization direction in accordance with an external magnetic field, and a nonmagnetic layer made of a Cu film magnetically isolating the magnetization-fixed layer and the magnetization-free layer, which are laid one upon another on at least a substrate. The method comprises: forming some layers, the last of which is the Cu film serving as the nonmagnetic layer, on the substrate by means of sputtering performed at a reduced pressure in a film-forming sputtering chamber; exposing gas-exposure chamber; and forming the remaining layers of the spin valve film, on the substrate, in the film-forming sputtering chamber.
The method uses two chambers, i.e., the film-forming sputtering chamber and the gas-exposure chamber. Thus, an extremely high vacuum can be maintained in the film-forming sputtering chamber, and the surfactant gas introduced into the gas-exposure chamber can retain a high repeatability.
In the film-forming sputtering chamber, some layers, the last of which is the Cu film serving as the nonmagnetic layer, are formed on the substrate. In the gas-exposure chamber, the substrate is exposed in an atmosphere of gas that activates a surface of the Cu film, thereby smoothing the surface of the Cu film. Additionally, the anti-ferromagnetic layer can be formed on the substrate in a higher vacuum than before.
The inter-layer coupling acting between the magnetization-fixed layer and the magnetization-free layer can therefore be suppressed even if the Cu film interposed between said layers and serving as a nonmagnetic layer is made thin. Further, the anti-ferromagnetic layer can acquire good characteristics. Hence, it is easy to manufacture a high-quality spin valve film that exhibits an improved rate of change in magnetoresistance.
To achieve the other object, a method is provided, which is designed to manufacture a magnetoresistance-effect magnetic head comprising a spin valve film as a magnetism-sensitive element for detecting magnetic signals emanating from magnetic recording media. The spin valve film comprises an anti-ferromagnetic layer, a magnetization-fixed layer magnetized in a prescribed direction by an exchange coupling magnetic field acting between it and the anti-ferromagnetic layer, a magnetization-free layer having a magnetization direction in accordance with an external magnetic field, and a nonmagnetic layer made of a Cu film magnetically isolating the magnetization-fixed layer and the magnetization-free layer, which are laid one upon another on at least a substrate. The method comprises forming the spin valve film by: forming some layers, the last of which is the Cu film serving as the nonmagnetic layer, on the substrate by means of sputtering performed at a reduced pressure in a film-forming sputtering chamber; exposing the substrate in a gas atmosphere in a gas-exposure chamber filled with gas that activates a surface of the Cu film; and forming the remaining layers of the spin valve film, on the substrate, in the film-forming sputtering chamber.
In the method of manufacturing a magnetoresistance-effect magnetic head according to the invention, two chambers are used, i.e., the film-forming sputtering chamber and the gas-exposure chamber, in forming the spin valve film. Thus, an extremely high vacuum can be maintained in the film-forming sputtering chamber, and the surfactant gas introduced into the gas-exposure chamber can retain a high repeatability.
In the film-forming sputtering chamber, some layers, the last of which is the Cu film serving as the nonmagnetic layer, are formed on the substrate. In the gas-exposure chamber, the substrate is exposed in an atmosphere of gas that activates a surface of the Cu film, thereby smoothing the surface of the Cu film. Additionally, the anti-ferromagnetic layer can be formed on the substrate in a higher vacuum than before.
The inter-layer coupling acting between the magnetization-fixed layer and the magnetization-free layer can therefore be suppressed even if the Cu film interposed between said layers and serving as a nonmagnetic layer is made thin. Moreover, the anti-ferromagnetic layer can acquire good characteristics. As a result, it is easy to manufacture a high-quality magnetoresistance-effect magnetic head that exhibits an improved rate of change in magnetoresistance of a spin valve film.
Other objects of the invention and the specific advantages of the invention will be more apparent from the following description of embodiments.